Collapsible rope or chain ladders with ridged rungs or steps are commonly used in the marine environment. Such ladders, sometimes known as a Jacob's ladder, may be rolled up or collapsed when not in use and thrown over and hung from the side of a vessel to provide access. The ladder rungs are typically constructed of a variety of materials and can be wood, metal or sometimes even polymer. Polymer materials are frequently utilized on rope ladders intended for a marine environment because the use of polymer materials minimizes damage to the ladder rung associated with corrosion or rot from the wet or saltwater conditions.
The use of polymer materials to construct the rungs of a collapsible rope ladder presents a number of problems. Among these problems is the reduced strength and increased deformation associated with polymer ladder rungs and the increase in weight of the polymer rung that is typically required to provide adequate rung strength and minimize rung deformation. These disadvantages are typically addressed by utilizing a hybrid rung made from polymer and an external or internal metal reinforcing frame. However, these solutions increase the expense and effectiveness of marine rope ladders that utilize polymer treads.
Further, in the design and construction of a typical molded part, with a plastic that contains internal reinforcement fibers, the part to be molded and molding process typically configured in order to minimize plastic flow path length through the part and pressure drop of injection plastic across the part as the plastic is injected into the mold during manufacture. Such a strategy minimizes injection time, temperature differentials and pressure differences within the part being constructed. However, a disadvantage of this strategy is that it does not provide sufficiently for a desired orientation of the reinforcement fibers in the plastic during molding of the part.
Consequently, a need exist for improvements in polymer ladder rungs and rung construction techniques in order to provide collapsible rope ladders having polymer rungs for a marine environment that minimize the disadvantages currently associated with rope ladders having polymer ladder rungs.